Callback State
name
Unique State name. Must follow the Serverless Workflow Naming Convention
string
yes
type
State type
string
yes
action
Defines the action to be executed
object
yes
eventRef
References an unique callback event name in the defined workflow events
string
yes
timeouts
State specific timeout settings
object
no
eventDataFilter
Callback event data filter definition
object
no
stateDataFilter
State data filter definition
object
no
onErrors
States error handling and retries definitions
array
no
transition
Next transition of the workflow after callback event has been received
string or object
yes (if end is not defined)
end
Is this state an end state
boolean or object
yes (if transition is not defined)
compensatedBy
Unique name of a workflow state which is responsible for compensation of this state
string
no
usedForCompensation
If true, this state is used to compensate another state. Default is false
boolean
no
metadata
Metadata information
object
no
Example:
Serverless orchestration can at times require manual steps/decisions to be made. While some work performed in a serverless workflow can be executed automatically, some decisions must involve manual steps (e.g., human decisions). The Callback state allows you to explicitly model manual decision steps during workflow execution.
The action property defines a function call that triggers an external activity/service. Once the action executes, the callback state will wait for a CloudEvent (defined via the eventRef property), which indicates the completion of the manual decision by the called service.
Note that the called decision service is responsible for emitting the callback CloudEvent indicating the completion of the decision and including the decision results as part of the event payload. This event must be correlated to the workflow instance using the callback events context attribute defined in the correlation property of the referenced Event Definition.
Once the completion (callback) event is received, the Callback state completes its execution and transitions to the next defined workflow state or completes workflow execution in case it is an end state.
The callback event payload is merged with the Callback state data and can be filtered via the "eventDataFilter" definition.
If the defined callback event has not been received during this time period, the state should transition to the next state or end workflow execution if it is an end state.
The timeouts property defines state specific timeout settings. Callback states can define the stateExecTimeout, actionExecTimeout, and eventTimeout properties. For more information on workflow timeouts reference the Workflow Timeouts section.
Note that transition and end properties are mutually exclusive, meaning that you cannot define both of them at the same time.
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